In a substrate processing apparatus such as a vertical film forming device or the like, a boat (a substrate holder) holding a plurality (several tens to one hundred and several tens) of substrates is accommodated within a process chamber and is heated while supplying a process gas. By setting the internal pressure and temperature of the process chamber at predetermined values, a film forming process is performed on the surfaces of the substrates by, for example, a CVD (Chemical Vapor Deposition) method.
In this substrate processing apparatus, it is sometimes the case that a two-boat system using two boats is employed in order to improve the operating efficiency of the apparatus. In the two-boat system, while the substrates held on one boat are processed within the process chamber, removal of processed substrates and mounting of unprocessed substrates are performed in the other boat. By doing so, the processing within the process chamber and the mounting and removal of the substrates to and from the boat can be performed in parallel. Thus, in the case of continuously performing the substrate processing, it is possible to improve the substrate processing efficiency. For example, Patent Document 1 listed below discloses a two-boat system in which a boat is designated depending on the individual difference between boats such as an attachment state of an impurity or the like and the content of a recipe and in which substrate processing is performed by carrying the designated boat into the process chamber.
When the substrates mounted to the boat are subjected to a film forming process, films are deposited on the boat as well as the substrates. If the film deposited on the boat has a thickness of a specified value or more, there appears an adverse effect in that the film is peeled off and dropped to become particles. For that reason, if the thickness of the film deposited on the boat reaches a predetermined threshold value, the boat is replaced by a new boat on which a film is not deposited.
In a vertical film forming device, a maintenance worker replaces a boat. Thus, in the case of replacing a boat, it is necessary to stop the device and to take a safety measure such as a measure of cooling the interior of the device and the boat in use. Furthermore, after replacing the boat, it is necessary to perform various kinds of adjustment and an operation check in order to normally operate the device. The works performed before and after the boat replacement are time-consuming. In the case of a vertical film forming device, about six hours are required. Accordingly, as the boat replacement period becomes shorter, the operating rate of the device is lowered and the production efficiency is reduced. Therefore, there is a need to efficiently perform the boat replacement work.
Patent Document 1 listed below discloses a single-substrate processing apparatus provided with a plurality of process chambers. In this apparatus, if the cumulative thickness value of the film deposited on the inner wall of at least one of a plurality of process chambers exceeds a threshold value, cleaning is performed in all the process chambers.